Method of applying wax to strands of glass fibers



METHOD OF APPLYING WAX TO STRANDS OF GLASS FIBERS Filed 001;. 20, 1958 FICA INVENTOR. Wary/v: ,4. lea/WWO: Q

ClARE/YCE m #518 States Patent METHOD OF APPLYING WAX TO STRANDS OF GLASS FIBERS Filed Oct. 20, 1958, Ser. No. 768,361

3 Claims. (Cl. 117-54) The present invention relates to methods of coating fibrous materials and it has particular relationship to methods of coating strands of glass fibers with wax or similar materials when the strands are wound on a tubular container. This application is a continuation-in-part of our copending application, Serial No. 432,114, filed May 25, 1954, now abandoned.

.Glass fiber strands coated and impregnated with wax are useful in the electrical industry, particularly as an insulator and filler in the manufacture'of wire and cable. The wax on the glass fibers makes it possible to twist, ply, Weave and braid the glass fibers without them becoming fuzzy and also the wax imparts moisture resistant characteristics to the fibers important in electrical use.

Glass fibers used in the electrical industry are mainly. in continuous filament strand form. Continuous filament strand glass fibers are produced by attenuating at a very high speed a large number of thin glass filaments, usually 204, from a bushing by mechanically winding them on a rapidly rotating spindle. The glass filaments are grouped into a single strand before being wound on the spindle.

At these high speeds of attenuation, for example'above 5,000 to 20,000 feet per minute, it is extremely difficult to get a sufiicient supply of wax on the individual filaments and strands during the attenuating operation. The

- electrical industry generally requires between 7 to percent by weight of wax thoroughly impregnated in the glass fiber strand. Thus, even though it is possible to apply some wax to the glass fiber strands bymeans of a pad or roller applicator during their attenuation, it has been found necessary to apply additional wax to the strands after they have been wound on a suitable container in strand form or after they have been twisted and/or plied together in yarn form.

A conventional method of applying wax to glass fiber strands or yarn is to wind the glass fiber strand or yarn on a perforated tube and dip the tube in a bath of molten Patented July 26, 1960 found that the vwax tended to channel out through the yarn directly from the perforations in the tube to the surface of the yarn package without flowing in all directions through the yarn to obtain uniform impregnation.

In accordance with the present invention it has been found that a glass fiber strand or yarn wound in layers on a perforated tube can be uniformly impregnated with wax by first drying the yarn package and then forcing the wax to flow through the glass yarn and then through the openings inthe tube by a differential in-pressure between the exterior and interior layers of yarn. The greater pressure is at the exterior layer and this differential in pressure causes the wax to flow evenly from all points on the surface of the yarn package into the perforated tube surface and then through the opening in the tube from where it is carried away. By forcing the wax to flow from the outer surface of the yarn package to the inner surface, it has been found that channeling does not occur as in the reverse procedure as described above.

'The wax is passed and recycled continuously through a plurality of yarn packages until the packages are all uniformly saturated. The uniform saturation does not take place upon the passage of the first amount of wax to flow through the yarn but rather occurs after a substantial amount of wax is recycled through the yarn. It has been 'observed that the coating procedure passes through several phases. The yarn on the tubes first becomes saturated but usually not uniformly so on all packages. Next, the amount of waxwhich is retained by the packages increases to a maximum while at the same time wax for several hours. After such soaking, several more to be due to the entrapment of moisture in the interior of the yarn package which moisture prevents the uniform impregnation of the wax throughout the package.

We have tried to immerse the yarn package and container in a vessel containing the wax under pressure. Here again, uniform impregnation could not be obtained because of the entrapment of moisture beneath the surface of the yarn package which moisture prevented the wax from flowing to all portions of the yarn.

We tried to overcome the problem of entrapped moisture by causing the wax to flow from the interior of a perforated tube through the perforations and out through the yarn wound on the tube. In this way it was hoped to drive out the moisture and thus obtain uniform impregnation 0f the yarn on the package. However, it was the difference in the extremes of the variation in wax content throughout the packages becomes smaller. Thereafter the amount of wax retained by the packages continues to become smaller and also the difference in the extremes of wax content in the various portions of the yarn package becomes smaller until the yarn package is uniformly saturated. An additional advantage which occurs from this procedure is that the yarn is easier to unwind from the package. This is because the uniformity of impregnation establishes uniform tension in the yarn during the unwinding process.

I The invention is further described in conjunctionlwith a description of the drawing in which: a

Fig. l is a diagrammatic view, partially in section illustrating an apparatus suitable for practice of the invention, and g a Fig. 2 is an enlarged portion of Fig. 1 further illustrating the flow of wax through a yarn packagein accordance with the invention. I

In the drawing a steel container 2 is shown for holding a supply of wax 4. The container is provided with an electrical heating element 6 which is connected by means of wires 8 to a source of electrical energy (not shown). The wax is maintained at a constant operating temperature by means of the heater element 6.

Y The heated liquid wax is moved through line 10 by means of pump, 12 to a cylindrical steel pressure tank 14'wherein it is applied to glass fiber yarn 16 wound on perforated tubes 18 having openings 20 in the sides thereof and having at least one end 22 open. The tubes 7 18 and'yarn 16 wound thereon are shown partially in elevation and partially in section in order to illustrate the openings 20 in the tubes. The tank 14 is made up .of two sections, upper section 24 and lower section 26,

smaller than the inside diameter of perforated tube 18 is mounted in conjunction with partition 28 in line with opening 30. The sleeve 32 has a flange 34 upon which .the tubes 18 may rest.

The upper end of section 24 of tank 14 is enclosed by means of lid 36 which'is hinged at 38 to the tank. The lid 36 is maintained tightly inplace by meansof bolt 40 screw-threaded into flange 42 forming the upper edge of section .24. Attached to lid 36 by means of spring 43 is a plate 44 which serves to hold perforated tubes 18 in place during the impregnating operation and also to close off the opening in the upper end of tubes 18.

Connected to the upper portion of section 24 is flow line 46 having pressure gauge 47 and pressure regulating valve 49 therein. This line serves to carry off the heated wax when the pressure within upper section 24 reaches a desired maximum as set in the valve 49. The wax is then returned to container 2 for reheating and recycling to the pressure tank.

The lower section 26 of the tank 14 serves as a reservoir to collect the liquid wax which has passed through the yarn and openings 20 in the tubes 18 and drained down the interior of the tubes 18 and through opening 30. Line 50 is connected to section 26 and it carries the wax back to container 2 for reheating and recycling.

The operation of the apparatus described above may be described in conjunction with the use of a perforated tube having wound thereon between 1% and 1% pounds of a glass fiber yarn designated as 150-1/0. This yarn is wound on a perforated paper twister tube so that the central portion of the yarn package is built up approximately parallel to the twister tube and each end of the package tapers out to the end of the tubes. The thickness of the glass fibers at the central portion is approximately inch. As shown, the yarn is wound with each turn essentially parallel to each adjacent turn, however, the invention is applicable to yarn wound in the form of small or large helixes around the tubes or to other types of windings.

The tubes containing the yarn are first placed in an oven of controlled humidity and heated at a temperature of 150 F. to 250 F. for a period ranging from 3 to 1 hours. This serves to reduce the moisture content of the yarn to a uniformly minimum amount so that uniform Waxing may be accomplished on a large number of packages. After removal of the moisture from the yarn, the tubes are then placed in the tank 14 with one end of each of the tubes fitting snugly over the sleeves 32 and resting on flanges 33. Lid 36 is then closed with plate 44 being held under positive pressure against the opening at the upper end of the tubes. Circulation of the wax may then be begun.

The circulation of the wax is described with respect to the use of paraflin wax, however, it is to be understood that this is merely exemplary and that other waxes and liquids may be circulated having similar properties and under similar conditions of flow rate, temperature, pressure, viscosity, etc. The wax is heated to a temperature in excess of its melting point, preferably about 250 to 350 F., in container 23. The wax at these temperatures has a viscosity of about 1 to 3 centipoises. It is then transported through line to pump 12 which pumps it into pressure vessel 14 where it is maintained at a constant pressure of about 15 pounds per square inch as regulated by pressure valve 49. The wax completely fills the upper section 24 of the pressure tank and surrounds the perforated tubes 18 having the glass yarn 16 wound thereon. The interior of the tubes 18 is connected to the atmosphere by means of opening 33 in sleeve 32, opening 39 in partition 28, lower section 26 and flow line 50.

The ditference in pressure between the wax in solution in section 24 and the interior of the tube 18 causes the wax to work its way through the glass fibers as indicated by arrows in Fig. 2 at all points along the surface of the wound yarn. It has been found that it is preferable to have a differential in pressure of about 12. to 18 pounds per square inch. Pressures lower than 12 pounds per square inch require longer waxing cycles.

The wax passes through the yarn until it reaches the surface of the tube upon which the yarn is supported and then passes along this surface to openings 20 in the tube through which it passes. The wax then drains down along the inside portion of the tube and through openings 33 and 30 into lower section 26 from whence it overflows into line 50 which carries it back to container 2.

The flow of wax through the yarn as thus described is continued for a time which is sutficient to insure uniform saturation of the yarn, which is arbitrarily considered to be a permissible variation from the maximum to the minimum content of wax on a number of tubes in the coating process of about 2 percent by weight or less. Tests have shown that this may require recycling of the wax for about 8 to 12 minutes during which time a total of about 7 to 10 pounds of wax is circulated through each tube of yarn and about 0.15 to 0.21 pound is applied to the individual filaments making up the strands forming the yarn.

A number of tests were performed and the data below illustrates the nature of the variations in wax content during the coating process. A number of packages were placed in a pressure vessel having a design as shown in Fig. 1 of the drawing and the vessel was filled with liquid paraffin wax heated to a temperature of 255 F. A hot wax was forced through the packages at a pressure of 15 pounds per square inch for various amounts of time to determine the amount and distribution of wax on the yarn at the various treating times. After the waxing treatment the packages were purged by forcing air at 300 F. and 40 pounds per square inch pressure from the outside of the package to the inside of the package for ten minutes.

Waxing treatments of one and one-half, three, six and twelve minutes were employed to determine the differences in amount and uniformity of wax content on the yarn. The distribution of wax on the yarn was obtained by unwinding a portion of the yarn at the outside, middle and inside of each package. The waxed yarn was weighed, heated to a temperature sufiicient to burn off the wax and then weighed again to determine the amount of wax on the yarn. The following results were obtained:

Table Waxing Percent Wax Range in Tube Time Average Percent No. (Min- Percent Wax utes) Wax (High to Outside Middle Inside Low) as as .0 e 9. 75 11. 03 0. as 77 As can be seen from the data in the table the wax on the yarn after a waxing time of 1 /2 minutes is fairly uniformly impregnated for some tubes but the variation from one tube to another is quite large and not satisfactory. As the recycling of the wax continues the average percent of wax on the tubes increases to a maximum at about 2 to 4 minutes while at the same time the difference in the extremes of variation in percent of wax from high to low on a number of tubes is decreasing. After six minutes of waxing, the average percent of wax is much lower than the maximum and the diflerence in the extremes of variation in percent of wax is decreasing toward the allowable variation. After a waxing period of about 8 to 12 minutes the average percent of wax has decreased to a minimum and the difference in the extremes of variation in percent of wax from the high to low amount present on the various tubes has been reduced to Within the allowable variation.

Although the present invention has been described With reference to specific details of certain embodiments thereof, it is not intended that such details be limitations on the scope of the invention except insofar as set forth in the accompanying claims. For example, glass fibers in other forms than 150-1/0 yarn may be coated with Wax or other materials. Likewise, the glass fibers may be wound or supported on the inside of a perforated tubular container such as a spinning bucket 9g supported on other supporting means than a perforated tube as shown and be coated in accordance with the various embodiments of the invention. Other modifications will be apparent to those skilled in the art.

We claim:

l. A method of applying wax to layers of strands of glass fibers supported on a hollow, tubular support having openings therein which comprises continuously passing molten wax through the layers of strands from the outside layer to the support and through the openings in the support until the strands are saturated with a maximum amount of wax and thereafter continuing the passage of wax through the strands until the amount of Wax on the strands is reduced and the difference between the high and low amounts of wax on the strands at different layers on the support is reduced.

2. A method of applying Wax to layers of strands of glass fibers supported on a hollow, tubular support having openings therein which comprises placing a plurality of the supports having the strands wound thereon in a pressure vessel, filling the vessel with liquid wax heated above its melting temperature, applying a pressure on the wax which is substantially greater than the pressure produced by the hydrostatic head of wax in the vessel so as to force the wax from the outside layer of strands to the tubular support and through the openings in the tubular support, continuously passing the Wax through the strands until they are saturated with a maximum amount of wax and thereafter continuing the passage of the wax through the strands until the amount of wax on the strands is reduced and the difference in the extremes of the variation in range of the high to low amount of wax on the strands on the various supports is reduced to the point Where the strands on the various supports are substantially uniformly impregnated.

3. A method of applying wax to layers of strands of glass fibers supported on a hollow, tubular support having openings therein which comprises drying the strands while on the support, placing the dried strands While on the support in a pressure vessel, filling the vessel with liquid wax heated to a temperature above its melting temperature, applying a pressure on the Wax Which is sub stantially greater than the pressure produced by the hydrostatic head of wax in the vessel so as to force the Wax from'the outside layer of strands through the layers of strands to the tubular support and through the openings in the tubular support, continuously recycling the wax through the strands until they are saturated with a maximum amount of wax and continuing the circulation of the Wax thereafter until the amount of wax on the strands is reduced and the difference in the extremes of variation in range of the high to low amount of wax on the strands is reduced to an amount such that the strands are substantially uniformly impregnated.

References Cited in the file of this patent UNITED STATES PATENTS 2,031,094 Brandwood Feb. 18, 1936 2,272,588 Simison Feb. 10, 1 942 2,340,048 Dykeman Jan. 25, 1944 

1. A METHOD OF APPLYING WAX TO LAYERS OF STRANDS OF GLASS FIBERS SUPPORTED ON A HOLLOW, TUBULAR SUPPORT HAVING OPENINGS THEREIN WHCH COMPRISES CONTINUOUSLY PASSING MOLTEN WAX THROUGH THE LAYERS OF STRANDS FROM THE OUTSIDE LAYER TO THE SUPPORT AND THROUGH THE OPENINGS IN THE SUPPORT UNTIL THE STRANDS ARE SATURATED WITH A MAXIMUM 